Are you talking about an autonomous AP right?
With regards to your case, you need to configure using the MBSSID setup,
ASSUME: VLAN20 MGMT VLAN
dot11 ssid VLAN119
vlan 19
authentication open -just a sample, configure as you desire
mbssid guest-mode
interface dot11radio 0
ssid VLAN19
mbssid
bridge-group 1 -already default, but just in case
interface dot11radio 0.19
encapsulation dot1q 19
bridge-group 2
interface gig0/0
encapsulation dot1q 19
bridge group 2
interface bvi 1
ip address 10.10.19.10 255.255.255.0 -ip mgmt of AP
*****
AT SWITCH
interface f0/1
switchport mode trunk
switchport trunk native vlan 20
pretty much explainable your WLAN traffic gets tag with VLAN19 and since the native vlan is 20,
well you guessed it you can manage your AP